The present invention relates to a fired ceramic having dense and low expansion characteristics and high strength.
Recently, various ceramics have been widely used in industries and in housewares. The condition in the uses of the ceramics become severe and the ceramics having high characteristics have been required in many cases.
The requirement for improving thermal shock resistance of the ceramic has been increased and various efforts for satisfying the requirement have been made.
For example, the strength of the ceramic has been increased so as to overcome a thermal stress caused by a thermal shock or the porosity of the ceramic has been increased to disperse the thermal stress or the extension of crackings in the ceramic has been prevented.
These methods have attained certain effects for satisfying the requirements. However, these methods have not been satisfactory to attain the requirements under severe conditions in the uses of the ceramics.
That is, the degree of increase of strength is limited. Sometimes, the resistance for preventing extension of crackings is weakened because of high strength, and accordingly, the increase of strength is not effective to high degree of thermal shock.
The increase of porosity of the ceramic causes decrease of the strength of the ceramic to limit the scope of the effective uses of the ceramics.
On the contrary, it has been paid attention to the ceramics having low thermal expansion characteristics because the ceramics do not have high thermal stress under severe thermal shock.
From the viewpoints of oxidation resistance at high temperature, oxide type ceramics having low thermal expansion characteristics have been preferably used.
The oxide type ceramic articles having required characteristics have been prepared by using the oxide type ceramics having low thermal expansion characteristics such as lithium aluminosilicates e.g. .beta.-spodumene (Li.sub.2 O.Al.sub.2 O.sub.3.4SiO.sub.2); cordierite (2MgO.2Al.sub.2 O.sub.3.5SiO.sub.2) and aluminum titanate (Al.sub.2 O.sub.3.TiO.sub.2).
However, in the conventional methods using these oxide type ceramics having low thermal expansion characteristics, a binder such as clay has been used in most of the applications from the viewpoints of fabricatability and strength of substrate. Accordingly, in order to prevent a softening in the firing so as to maintain a desired shape, it has been difficult to increase the temperature in the firing. Thus, the resulting fired products have high porosity and have not enough strength.